It is necessary to incorporate a counterbalancing force against the total weight of an overhead door to overcome the force necessary to raise the door. Such counterbalancing force may be provided by an extension-type spring in the lift track of the door, or more commonly, a torsion spring from which the door is fully suspended. Torsion springs store, as potential energy, all of the door's weight as a torsional wind on the spring. The torsion spring is mounted to a tapered, helically-groove body or "cone", which when threaded into the end of the spring, expands the spring inside diameter beyond its normal size thus creating torsional lock upon its cone. The torsion spring is coiled around a rotatably mounted horizontal shaft with one end of the spring being mounted to a non-rotating and rigidly mounted stationary cone. The other end of the spring is fitted with a winding cone. When the spring has been wound to its proper amount of turns by the winding cone, the cone is then locked to the shaft with set screws. A cable drum is also mounted on the shaft and the door is suspended by cables wound around the drums. As the door is lowered, the cable unwinds from the drum causing rotation of the shaft. Torsion force is thus applied to the torsion spring, a force which then helps to overcome the weight of the door when it is later raised.
Because of the mounting of the torsion spring on the tapered cone, it is inherent in its design that the spring will become tightly locked into the helical grooves of the cone through repeated, cyclic use. When it becomes necessary to remove the spring, the tight locking of the spring to the cone makes such disassembly extremely difficult or impossible, often entailing the destruction the the cone. Springs are usually mounted in pairs sharing a common stationary double mounting cone which is relatively expensive to replace.
The problem of spring removal has been addressed using a a torch, slip-jointed pliers, hammer and chisel, pipe wrenches and spanner wrenches. Torches almost always destroy the cone because cones are usually made of sand cast or die cast aluminum. Slip-joint pliers and pipe wrenches are often useless because of limited working clearance so that they can not be effectively applied to the terminal end of the spring.
A hammer and chisel are sometimes effective for spring removal if the terminal end of said spring, especially on the double stationary mounting cone, is in a suitable position so that the necessary blow to break the spring loose from its cone can be delivered. However, when the terminal end of one of the springs can not be accessed due to clearance limitations, the matching torsion spring must be unwound and the entire torsion shaft, springs, and cable drums must be dismantled and removed in order to repair or replace one spring.
Spanner wrenches which are primarily designed for the removal of notched spanner nuts are not suitable because there is no provision to prevent tangential or lateral movement of the claw resulting in tool slippage. Furthermore, conventional spanner wrenches, whether fixed or adjustable, tighten in a clamping action around the spring, making removal even more difficult.
U.S. Pat. No. 4,142,283 describes a wrench which is specially adapted for use in removing torsion springs from a winding cone. The wrench comprises a ring or C-shaped collar and a radially-oriented adjustable pin. In use, the collar is placed around the spring and cone and the pin is adjusted so as to engage the terminal end of the spring on the cone. Torque is then applied to the ring by a lever arm in order to overcome the torsion lock which the spring has developed on the cone through use.
While this specialized tool is an improvement over the use of a pipe wrench or the like, the fixed ring or C-shape of the wrench requires that the user have a number of variously sized C-rings available in order to accomodate cones and springs of different diameters. Additionally, this C-ring wrench requires free access over a coneless end of a spring for removal. If the spring is not broken and cone removal is desired, the spring must be cut with a torch to achieve access to cone. Finally, a radially-oriented pin the collar is used to apply a tangentially directed force against the terminal end of the spring. This is an ineffective means of force transfer because it does not lift the spring's terminal end from cone, thus resulting in the probable gouging of cone and damaging of the threads.
Spanner-type wrenches are also known. U.S. Pat. Nos. 1,504,847 and 1,528,691 are typical of spanner wrenches adapted to remove large diameter threaded nuts from a threaded cylindrical body. In operation, these spanner wrenches apply a tangentially-directed force to a notch in the nut through the action of a claw or pawl engaging the notch. The claw or pawl is generally flexibly connected to a lever arm which engages the opposite side of the nut and forms a fulcrum against which torque is applied to the device along the lever arm. The aforementioned U.S. Pat. No. 1,528,691 adds a feature of length adjustability to the claw connection to the lever arm in order to accomodate nuts of different diameters with the same wrench.
A major concern in the use of any of these devices is operator safety. The sudden breaking or release of a wrench or chisel or plier can result in direct injury to arms and hands of the operator as well as injury from objects propelled by the spring itself. None of the above devices positively engages the spring end to prevent lateral or radial slippage and release of the spring end once torque is applied.